1. Field of the Invention
The present invention relates to an illumination apparatus in which the light-condensing performance thereof is high and which is high-intensity and compact, and to an image projection apparatus using such an illumination apparatus.
2. Description of the Related Art
Conventionally, as a light-condensing illumination apparatus efficiently illuminating a specific place, for example, a vehicle headlamp, a floodlight, a spotlight, a flashlight, an illumination unit for a data projector, and the like have been known. In the light-condensing illumination apparatus, generally, an attempt is made to effectively carry out condensing illumination by a relatively simple method in which a light-emitting source which is relatively more similar to a point light source is reflected by a reflecting unit in which the reflecting shape thereof is contrived, and the directivity of luminous flux of the reflected light is improved by an optical lens or the like.
In the same way as in the general illumination, in these light-condensing illumination apparatuses as well, the demand that a size of the apparatus itself is not especially made large, and the light-condensing performance is improved, and an attempt is made to obtain even brighter illumination light is high. However, generally, there is the trend that the size of the light-condensing illumination apparatus is made large in order to obtain the even brighter illumination light. In particular, output power is enhanced due to applied electric power of a light-emitting source being made large, or a reflecting unit or an optical lens which is relatively enlarged is applied to the light-emitting source in order to improve the light-condensing performance thereof. Accordingly, in order to obtain brightness at a high light-condensing efficiency, the size of the illumination apparatus must be necessarily larger with respect to the light-emitting source. In other words, provided that there is a compact light-emitting source which outputs high power and which is similar to a point light source, the entire illumination apparatus can be made compact. In accordance with such a demand, making a conventional system light-emitting source compact has been developed, and in particular, an electric-discharging type compact light-emitting source which can output high power is presently advantageous means. However, there are a large number of problems such that even a compact electric-discharging type light-emitting source requires to be driven by a high voltage power supply in which it is difficult to make the circuit dimensions small, or the like, for making an entire illumination apparatus compact, and it is said that the method in which an entire illumination apparatus is made compact substantially realize limit.
On the other hand, as the next-generation compact light-emitting source, a light emitting diode (hereinafter, referred to as LED) has been recently markedly focused on. Up to the present, although the LED has merits such as a compactness, high resistance, a long life, or the like, the major applications are for using as a indicator illumination for various meters and a confirming lamp in a control state due to the limitations of the light-emitting efficiency and the light-emitting output. However, in recent years, the light-emitting efficiency has been being rapidly improved, and it has been said that the light-emitting efficiency of the LED exceeds the light-emitting efficiency of an electric-discharging type high-pressure mercury lamp and a fluorescent lamp which have been conventionally considered as the highest efficiency, is only a question of time. In accordance with an appearance of the high-efficiency and high-intensity LED, a high power light-emitting source by the LED has been rapidly close to be realized. Further, the application of the LED has been accelerated by the fact that the stage of practical use for the blue LED in addition to the conventional red and green LEDs is recently achieved. In reality, due to the plurality of high-efficiency and high-intensity LEDs being used, putting the LEDs to practical use for traffic lights, an outdoor type large full color display, various lamps of an automobile, a back light of liquid-crystal display of a cellular phone, has been started.
As a promising compact light-emitting source of an illumination apparatus for which light-condensing performance is required as well, it is considered that the high-efficiency and high-intensity LED is applied. The LED originally has characteristics superior than the other light-emitting sources in the points of a life, durability, a lighting speed, simplicity of a lighting driving circuit. In particular, the applicable range as a full color image display apparatus is enlarged due to three primary colors being completed as a light-emitting source emitting light by itself due to blue color being added. As a typical example of the illumination apparatus for which light-condensing performance is required, for example, there is a projector display apparatus (image projection apparatus) in which a display image is formed from image data, and the display image is projected. In a conventional image projector apparatus, desired primary colors are separated from a white system light-emitting source by a color filter or the like, and space light modulation is applied to image data corresponding to each color, and color image display has been able to be realized due to the image data being three-dimensionally and temporally synthesized. When the white system light-emitting source is used, because only one desired color is separated and used, there are a large number of cases in which colors other than the separated color are wastefully thrown away. In this point, because the LED emits the desired light itself, it is possible to emit a required quantity of light as needed, and it is possible to efficiently utilize the light of the light-emitting source without light being wasted as compared with the case of the conventional white system light-emitting source.
Focusing on such superior applicable conditions of the LED, examples in which the LED is applied to an illumination apparatus for an image projection apparatus are disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-32278, U.S. Pat. Nos. 6,227,669B1, 6,318,863, or the like. In the technique disclosed in these publications, a certain quantity of light is insured by structuring a plurality of LEDs, and some of luminous flux from the individual light-emitting sources are condensed by an optical element such as an optical lens or the like, and the luminous flux is controlled so as to be successfully within an incident angle allowed by a light-modulating element irradiating the light. In an optical modulating element such as a liquid crystal device which is generally and broadly used, because an incident angle allowed as illumination light is extremely small, it is considered as an ideal, not only to have mere light-condensing performance, but also to form a luminous flux having a higher parallelism and irradiate the luminous flux. This is markedly important point from the standpoint in which efficiency for light utilization in an optical modulating element is improved.
As such light-condensing means for guiding the outgoing light from the LED to a predetermined direction, for example, a specific shaped prism is proposed in U.S. Pat. No. 4,767,172.